Within a computer system, numerous techniques exist for inputting data and commands from a user to the computer system. One technique is to use a special computer "pen" for entering information via a display screen of a computer system. A user moves the pen around on the screen, inputting or selecting information to be transmitted to the computer system.
A variety of technologies exist for inputting information to a computer system using a pen. One such technique uses a special pen in conjunction with an electromagnetic pen digitizer that is placed behind the display unit of a computer system. By moving the pen around on the glass screen of a display unit, and/or by pressing the pen against the glass screen, the electromagnetic pen digitizer is able to receive information from the pen and transmit this information to the computer system. The pen is able to transmit information using electromagnetic signals that are picked up by antenna on the digitizer. One advantage of using an electromagnetic pen digitizer is that this technology is able to input information from the pen such as its X, Y coordinates on the display, pen button status, the tilt of the pen and the pressure of the pen on the glass screen. Such electromagnetic pen digitizers are especially useful in (but not limited to) flat panel display assemblies of a portable computer.
As shown in FIG. 1, electromagnetic pen digitizers to date have been assembled with flat panel displays simply by placing a discrete digitizer implemented using standard printed circuit board technology completely behind the flat panel display (including being behind the diffuser backlight and behind the active display electronics). FIG. 1 shows a display unit 10 of a computer system having a flat panel display assembly 12 and an electromagnetic pen digitizer 14. Digitizer 14 is a standard electromagnetic pen digitizer. Display 12 includes viewable area 16 through which information is presented to the user and through which the user may input information, and an outside side area 18 that is not used for presenting or inputting information. In older generations of flat panel displays, side area 18 is relatively large compared to viewable area 16 and incorporates the active display electronics 20 that control the presentation of information on viewable area 16 of display 12.
As can be seen in FIG. 2, active display electronics 20 are located in side area 18 outside of viewable area 16 of display 12. Thus, because side area 18 is relatively large compared to viewable area 16, electronics 20 are easily incorporated to the side of viewable area 16. Thus, electronics 20 do not interfere with the interaction between a special pen moving on viewable area 16 and electromagnetic pen digitizer 14 located behind display 12. In other words, having electronics 20 to the side of area 16 prevents electronics 20 from interfering with electromagnetic signals between the pen and the digitizer. Such a design for a display unit is workable, although viewable area 16 may be relatively small.
As flat panel display technology moves forward, the overall size of a display unit has been shrinking due to designs in which the active display electronics are located directly behind the viewable area of the display. By locating the active electronics behind the viewable area, space is saved at the sides of a flat panel display assembly and allows for an overall smaller package. Also, as the side areas of a flat panel display assembly are no longer needed to incorporate the active display electronics, the viewable area of the display may also be made larger, with attendant advantages for a user.
FIG. 3 illustrates an example of a display unit in which the active display electronics are placed behind the viewable area of the display. Shown is a display unit 30 having a flat panel display assembly 32, a viewable area 36, side area 38 and active display electronics 40. As electronics 40 are now located directly behind viewable area 36, side area 38 may now be made much smaller relative to viewable area 36. Thus, the overall size of display unit 30 may be reduced, or alternatively, the size of viewable area 36 may be increased. Each of these alternatives has various advantages. One technique for locating electronics 40 behind viewable area 36 literally "folds" the electronics in behind viewable area 36. This technique, often referred to as "bent TAB" or "folded TAB", uses a printed circuit board attached via flexible ribbon cable ("flex cable") to the mother glass of the flat panel display assembly. Attached to the flex cable are a number of integrated circuit drivers that are attached using tape-automated bonding (TAB) construction technology. This "bent TAB" technique allows active electronics 40 to be placed behind viewable area 36. Of course, other techniques aside from "bent TAB" may be used in order to place the active electronics behind a viewable area.
Unfortunately, attempting to place a discrete electromagnetic pen digitizer behind a flat panel display assembly that includes active electronics behind the viewable area is not possible due to the interference of the electromagnetic energy and the electromagnetic shielding induced by the active electronics. In other words, when the active electronics are located directly in front of a discrete electromagnetic pen digitizer, the electromagnetic signals between a pen on the display screen and the digitizer are blocked or distorted by the electronics.
FIG. 4 illustrates a display unit 50 in which this situation occurs. Flat panel display assembly 32 has a viewable area 36, side areas 38 and active display electronics 40. Active electronics 40 are located in between viewable area 36 and an electromagnetic pen digitizer 34. Electronics 40 interfere with communication between pen 52 and digitizer 34.
Digitizer 34 is basically a sensor panel that includes numerous antenna for receiving a signal from pen 52, and may also serve as a power source for pen 52. In operation, digitizer 34 sends an energy pulse to pen 52 which receives power for operation from the energy pulse, or is triggered by the energy pulse to transmit for pen battery systems. Pen 52 is then able to transmit information such as pen button status and pressure to digitizer 34 by broadcasting a relatively weak electromagnetic signal. Digitizer 34 derives location and tilt of the pen by looking at the relative signal strengths from the antennas in the digitizer. Because the signal is relatively weak, electronics 40 create interference. Although various manufacturers have attempted to solve this problem (such as by changing the frequency of the pen, by increasing signal strength via a pen battery, by decreasing maximum pen resolution or by reducing the active pen area), a workable solution for this type of display assembly is yet to be found. Therefore, display units that include a flat panel display assembly along with an electromagnetic pen digitizer are typically only implemented with a small viewable area and a large side area in which the active electronics are incorporated. Large viewable areas of display units such as is shown in FIG. 3 that are made possible with technologies such as "bent TAB" have proven extremely difficult to use with an electromagnetic pen digitizer.
Other types of digitizers for detecting the location of a pen on a screen are in use, but these have a variety of disadvantages. For example, a resistive membrane may be placed on top of a flat panel display assembly. However, because this membrane is placed on top of the display, less light is transmitted, and more power is needed to increase light from the backlight unit. However, this technique is not well suited for a portable computer having a flat panel display where power is at a premium. Another technique uses electrostatic capacitance in which an indium tin oxide (ITO) conductive film is also placed on top of the display. Similar to the previous problem, because this film is on top of the display, it reduces the light transmitted and more power is required. In addition, this conductive film is implemented as a grid upon the display which also causes interference with the display of information to a user. Also, these techniques only supply the pen location and pen button status and not tilt or pressure. An electromagnetic pen digitizer is more desirable as it is able to receive and to derive much more information from a broadcasting pen. For example, tilt is not obtained from the pen, but is calculated from the digitizer sensor panel.
Another technique uses LED lights around the perimeter of a screen which indicate the location of a pen when their light path is broken. However, in addition to not providing tilt or pressure information (only X,Y coordinates), the resolution provided by this technique is too low for acceptable use on a high definition flat panel display. Thus, although other digitizers aside from an electromagnetic digitizer may be used, each has a variety of drawbacks. An electromagnetic digitizer is able to provide location, tilt and pressure information which is advantageous in many situations.
Therefore, it is desirable to provide a technique by which an electromagnetic pen digitizer may be used with a flat panel display assembly having electronics behind a viewable area. It is further desirable that such a technique have the lowest fiscal and manufacturing impact to existing flat panel display assemblies in order to avoid potentially large capital costs and development time required to develop a flat panel display assembly that is custom built for use with an electromagnetic pen digitizer.